The present invention relates to a method and a device for displaying flight parameters on an aircraft, especially a transport airplane. This display device is capable of representing a dialog device allowing dialog between an operator of the aircraft, in particular a pilot, and a system for guidance of said aircraft.
It is known that aircraft furnished with a guidance system, namely either a flight director which calculates piloting setpoints as a function of guidance setpoints or an automatic piloting system which makes it possible to follow guidance setpoints in an automatic manner, are provided with an overview (or summary) of the behavior of this guidance system which allows the pilot of the aircraft to ascertain the aircraft guidance modes.
An overview of the behavior of the guidance system (flight director or automatic piloting system, possibly associated with automatic thrust control) is effected, in general, on the screens displaying the primary flight parameters, of PFD (“Primary Flight Display”) type, at the level of a table of FMA (“Flight Mode Annunciator”) type. This overview summarizes, generally, the guidance modes engaged (active) on each axis (speed, lateral, vertical), as well as the armed guidance modes, that is to say those which have been requested by the pilot and which will engage automatically when mode engagement conditions are fulfilled. By way of example, away from the trajectory of the flight plan, in the mode for holding heading converging toward the trajectory of the flight plan with the flight plan trajectory capture and holding mode armed, the latter mode engages automatically on approach to the flight plan.
By way of non-exhaustive example, the guidance modes taken into account in the table of FMA type can be the following:                mode of the auto-throttle:        
“THRUST”: mode commanding a fixed thrust;
“SPEED”: mode commanding a variable thrust making it possible to uphold an air speed setpoint (CAS) or MACH setpoint, etc.;                vertical mode:        
“OP CLB”: mode of climbing toward a setpoint altitude with a fixed thrust while complying with an air speed (CAS);
“OP DES”: mode of descending toward a setpoint altitude with a reduced fixed thrust while complying with an air speed (CAS);
“VS”: mode of holding of a vertical (climb or descent) speed;
“FPA”: mode of (climb or descent) slope holding;
“G/S”: mode of tracking a vertical axis corresponding to an approach beam, etc.;                lateral mode:        
“HDG”: heading capture and holding mode (HEADING);
“TRK”: course capture and holding mode (TRACK);
“NAV”: flight plan tracking mode (route);
“LOC”: mode of tracking a lateral axis corresponding to an approach beam, etc.;                category of approach (indicating, inter alia, whether or not an automatic landing is possible depending on the state of the onboard systems); and        state of the functions (indicating the state of engagement of the guidance systems such as the automatic piloting system, the flight director, the automatic thrust management).        
Moreover, the engaged (active) modes and also the armed modes are indicated to the pilot by the table of FMA type.
By virtue of this textual summary of the present (engaged) and forthcoming (armed) guidance modes, the pilot has an overview of the objectives taken into account by the guidance system.
In order to supplement this picture, the pilot will thereafter look at the guidance setpoints associated with the guidance modes on the PFD screen, as well as the current flight parameters. These two values (current value and setpoint value) are displayed on one and the same scale making it possible to see their relative positions (inter alia), and their positions with respect to characteristic values (for example characteristic speeds on the speed scale).
In the mode of climbing toward an altitude, the value of the altitude setpoint taken into account by the system lies on the altitude scale of the PFD screen.
The set made up of the FMA table and of the PFD screen affords the pilot access to a complete picture of the behavior of the guidance system.
The FMA table provides a textual summary which requires a learning on the part of the pilots so as to associate the behavior of a mode with its textual label. For example, with this type of textual retrieval, the pilot must know (learn) that, for the label “OP CLB”, the behavior of the mode is that of a climb with no altitude constraint to a flight level, with a fixed thrust for the engines (on the “Climb” level), while complying with an air speed (CAS). On the other hand, the “CLB” mode will indicate compliance with the altitude constraints on the climb if appropriate.